1. Field of the Invention
This invention relates to a disk holding device for holding a disk medium so as to rotate the same, the disk holding device being used in an optical disk drive unit which records and reproduces information relative to the disk medium by light or light-magnetism.
2. Description of the Related Art
Recently, remarkable progress has been made in techniques relating to of recording and reproducing information by the use of light. Examples of read-only optical devices include a so-called CD (compact disk), a CD-ROM and a laser disk. Read-write optical devices have now been extensively used in secondary memory devices of computers, rewritable filing devices and so on. Large-capacity optical disk are devices, such as DVDs (digital versatile disk), are expected to become a mainstream product in the future.
There exist various optical disk standards having respective features. These have been developed to meet requirements for performance and also because of differences in the time of development of the technologies. However, the existence of the various optical disk standards and the sacrifice of their interchangeability are disadvantageous in the handling of these optical disks and the extension of the market. Particularly, CDs and DVDs, which both have created a large market in homes and so on, and have almost the same appearance in the form of a disk having a diameter of 12 cm, are not optically interchangeable with each other. As a result, the DVD disk can not be reproduced by a CD player, and the opposite is the same. This is due to differences in (1) thickness of a disk plate (CD is 1.2 mm thick, and DVD consists of two 0.6 mm-thick plates laminated together), (2) characteristics of objective lenses, (3) wavelength of laser beams to be used, and recording density (the DVD is higher in density than the CD).
In the market, there has been an increasing requirement that the two different disks, that is, the CD and the DVD, which have different standards, respectively, should be used in a common disk drive. A conventional disk holding device, which has been provided to meet this requirement, and is capable of holding such two different optical disks, will now be described with reference to the drawings. Generally, conventional disk holding devices are classified into a clamp type (disclosed for example in Japanese Patent No. 1509217) Japanese Patent Application No. 63-60459), in which a disk is clamped and held between two mechanism portions, and a self-holding type in which, when a disk is placed on a table, its holding mechanism holds the disk. In order to achieve a small-size and thin design of the disk drive unit, the self-holding type is advantageous. The disk holding device of the self-holding type will be described below.
FIG. 25 is a view showing the construction of the conventional disk holding device of the self-holding type. In FIG. 25, a disk holding mechanism portion 30 capable of self-holding a disk 23 will be described. In FIG. 25, a spindle motor 34 is broadly divided into a turntable unit 36 for holding the disk 23 and a drive portion 40 for rotating the disk 23.
Reference is first made to the turntable unit 36. When holding the disk 23, claw-like members 26 first interfere with an inner peripheral edge of the disk 23. The claw-like members 26 are provided at at least three portions of a turntable 21. Each of the claw-like members 26 is urged radially outwardly (that is, toward the outer periphery) by a resilient member 27, and bosses (not shown), provided respectively on opposite sides of the claw-like member 26, are supported respectively by guides (not shown) of a center hub 25.
On the other hand, the drive portion 40 mainly constitutes a magnetic circuit, and consists of a rotor yoke 37, magnets 38, a coil 39, a back yoke 42, and a bearing metal unit 41 supporting a spindle shaft 24 press-fitted into the turntable 21. The spindle shaft 24 is rotatably supported on a thrust bearing 46. Hall elements 47 are mounted on an FPC 48 provided on the surface of the back yoke 42, and are opposed to the magnets 38, respectively. In this embodiment, although the spindle motor is of the peripherally-opposed type, it may be of the surface-opposed type in which case the same functions are achieved.
FIGS. 26A and 26B are illustrations of the operation of the disk holding mechanism portion 30 of FIG. 25. In FIGS. 26A and 26B, for loading the disk 23, the disk 23 is pressed respectively against rounded portions 26b of the claw-like members 26 (provided at at least three portions of the turntable 21) from the upper side, and is placed on the turntable 21. At this time, each claw-like member 26 is retracted by the disk 23 against the bias of the resilient member 27 to slide toward the inner periphery of the center hub 25 along the guides in the center hub 25.
Thus, the inner peripheral edge of the disk 23 moves past the claw-like members 26 while pressing the rounded portions 26b of these claw-like members 26. The disk 23 is pushed until it is brought into intimate contact with a slip sheet 22 bonded to the turntable 21.
When the inner peripheral edge of the disk 23 thus moves past the claw-like members 26, the claw-like members 26 are extended or projected under the influence of the resilient members 27, so that a lower slanting surface of the rounded portion 26 of each claw-like member 26 abuts against the inner peripheral edge of the disk 23. As a result, the disk 23 is self-held by the claw-like members 26 provided respectively at at least three portions of the turntable 21. At this time, even if the disk 23 is eccentric with respect to the spindle shaft 24, the disk 23 is held by the urging force of the claw-like members 26 held against the disk 23, and is rotated by the drive portion 40.
Next, a disk holding device of the clamp type will be described, and a countermeasure to the above-noted eccentricity will also be described. FIG. 27 is a view showing the construction of the disk holding device of the clamp type. A turntable unit 36 for clamping a disk 23 will be described with reference to FIG. 27. In FIG. 27, a center boss 45 is provided at the center of a magnet clamper 44 having a magnet (not shown) embedded therein. The center boss 45 is engaged with a spindle shaft 24. When the magnet clamper 44 is closed, the magnet in the magnet clamper 44 produces a magnetic attraction force relative to a ferromagnetic member (e.g. iron plate) embedded in a cone ring 28. The precision of the center position of the disk is maintained by the center boss 45 of the magnet clamper 44. The disk 23 is pressed against a turntable 21 uniformly over an entire surface thereof.
A disk alignment mechanism portion for aligning the disk 23 so as to overcome the above eccentricity problem will be described with reference to FIG. 27. The turntable unit 36, having the disk alignment mechanism portion 31 mounted therein, is mounted on the spindle shaft 24. More specifically, the spindle shaft 24 is press-fitted in the turntable 21. The cone ring 28 is slidably mounted on the turntable 21, and is urged in a disk-unloading direction by a return coil spring 29. The sliding movement of the cone ring 28 is limited by a C-ring 43. That surface of the cone ring 28 for engagement with the inner peripheral edge of the disk 23 is formed into a substantially conical surface which is tapered, that is, decreasing in diameter progressively in the disk-unloading direction.
First, the disk 23 is placed on the disk alignment mechanism portion 31 of the above construction, and when the magnet clamper 44 is closed, the surface of the disk 23 is pressed against the turntable 21 as described above, and during this operation, the inner peripheral edge of the disk 23 slides along the conical surface of the cone ring 28. As a result, the disk 23 can be aligned while being accurately held in position.
In order that the above conventional disk holding devices can hold a CD and a DVD different in plate thickness from each other, and also can have a small-size and thin design, it is necessary that the disk holding device can self-hold the disk while aligning the disk. However, the reduction of the thickness of the turntable (base member) adversely affects the rigidity and the rotation accuracy particularly when the turntable is made of a resin material. Moreover, when the mechanism portion capable of self-holding and aligning the disk is mounted on the turntable, it has been difficult to reduce the thickness of the disk holding device in a direction of the thickness of the disk.
Under these circumstances, the disk holding device has now been required to be capable of holding a CD and a DVD and also to have such a small-size and thin design as to be mounted in a mobile computer.